Laminated metal electrodes and method for producing the same



May 6, 1969 GWYNN ET AL LAMINATED METAL ELECTRODES AND METHOD FORPRODUCING THE SAME Filed Jan. 14, 1966 M rrryl INVENTORS Ross M. 6wY/v/vM v ATTORNEY United States Patent 3,443,055 LAMINATED METAL ELECTRODESAND METHOD FOR PRQDUCING THE SAME Ross M. Gwynn, 916 Dornajo Way 95825,and Tim Therny, 7025 Uranus Parkway 95823, both of Sacramento, Calif.

Filed Jan. 14, 1966, Ser. No. 520,596 Int. Cl. B23k 11/06 U.S. Cl.219-83 20 Claims ABSTRACT OF THE DISCLOSURE A superior electrode,uniquely durable in chlorinating, hypochlorinating and relatedelectrolytic processes comprising a laminated body of platinum metalfoil bonded to a compatible metal substrate which is highly resistant toelectrolytic oxidation, the bonding being effected by applying along aline of contact between a small diameter cylindrical member of hardconductive metal, rotatable in a massive electric conductor, inengagement with said foil, and a second massive electric conductor inengagement with said substrate, a pressure of about 10 to 300 pounds perlinear inch, and an electric current below 12 volts at an amperage toprovide at least 3 kva. per linear inch of said line of contact, whileadvancing said small diameter cylindrical member in a directionperpendicular to said line of contact at a rate to provide a bondingheat sufficient to soften, without melting, the substrate surface.

The platinum metal can be platinum, rhodium, iridium or ruthenium oralloys thereof; the substrate metal can be tantalum, titanium, niobiumor alloys thereof; and the bonding is preferably efi'ected at a pressureof 50 to 150 pounds per linear inch, using direct current of 0.1 to 5volts at an amperage to provide 7 to 100- kva. per linear inch.

In electrolytic processes generally, and particularly in theelectrolysis of chlorides and the production of hypochlorites orpercompounds, intense corrosion can be encountered at the anode unlesssuitably resistant materials are employed in such anodes. Even with anormally resistant metal such as tantalum or titanium the action ofchlorine being liberated at the anode so alters or oxidizes the metalsurface as to rapidly reduce its electric conductivity or increase itsovervoltage, thus impairing its usefulness as an anode.

Materials which are found most advantageous from the standpoint of bothchemical resistance and electric conductivity comprise the metals of theplatinum group, including in particular ruthenium, rhodium, iridium, andplatinum, and mixtuers and alloys thereof. Unfortunately the scarcityand cost of such metals prevents their use as anodes for mostelectrolytic processes except as such metals are applied in thin layersor foils to less expensive supporting materials.

Various methods have been used in the past in attempts to suitably coata substrate, such as tantalum, niobium, titanium, and alloys thereof,with metals of the platinum group, but with varying degrees of successand practicability. United States Patent No. 2,719,797, for example,discloses chemical decomposition or electrolysis to form thin depositsof platinum metals, in conjunction with heating to effect a bond withthe substrate. These methods, however, tend to produce uneven orincomplete coatings of the platinum metal, and there is a substantialtendency for the heat treatment to modify the platinum metal compositionand its electric conductivity, thereby reducing its effectiveness as ananode surface material.

It is pointed out in said United States Patent No. 2,719,797 thatattempts to cover the tantalum strip with a platinum metal foil to holdthe metals together, as by Patented May 6, 1969 sweating, rolling orhammering, have proved to be unsatisfactory because the platinum metalfoil is held to the tantalum only by mechanical contacts which is notsufficient to permit its use as an anode.

It is now discovered in accordance with the present invention that thetype of intimate bond of platinum metals with titanium or othersubstrate indicated to be desirable but difficulty obtainable in UnitedStates Patent No. 2,719,797 can be achieved in a practical andeconomical way by bonding platinum metal foil to tantalum, titanium,niobium or other suitable substrate material under the influence ofpressure and locally generated thermoelectric heat. The substratesurface preferably is prepared for bonding as for example by beingroughened slightly to exhibit a matte appearance. A clean matte surface,free of oxide, organic residues, and excess adsorbed gases improvesbonding and minimizes the chance of blister formation. Bonding can befurther enhanced if desired, by applying to the cleaned matte surface,suitably by electrolitic disposition, a very thin coating of' palladium,silver, or other soft chlor-resisting solder-type metal which will aidin alloy formation at the interface between the substrate and foil.

In carrying out the new method a cleaned or prepared plate of tantalum,titanium, or niobium or other substrate material is disposed in bearingengagement with a massive electric conductor with a sheet of platinummetal foil, suitably of a thickness within the range of about 0.0003 to0.002. inch, overlying the opposed face of said plate. A second somewhatsmaller massive conductor grooved to rotatably receive a hard,small-diameter, cylindrical conducting element is then brought intobearing engagement with the foil-substrate assemblage and pressure isapplied to provide a pressure of 10' to 300 pounds and suitably 50 to150 pounds per linear inch of contact between said cylindrical elementand supported foilsubstrate assemblage. While maintaining this pressureand slowly advancing said line of contact in a direction perpendicularto the axis of said element a low voltage, high amperage current isapplied across said massive conductors to create a very highelectrothermal intensity along said line of contact to bond the foil andsubstrate. The voltage should preferably be below 12 volts and suitablywithin the range of about 0.1 to 5 volts, and the amperage sufficientlyhigh to provide a current in excess of 3, and preferably within therange of about 7 to kva. (kilovoltamperes) per linear inch along saidline of contact. Either direct or alternating current can be used forthe bonding, but direct current is preferred.

In order to avoid mechanical damage to the delicate foil, thecylindrical element, which may be tungsten, tungsten carbide, alloys oftungsten carbide with small amounts, i.e., less than 25%, of an alloyingmetal selected from the group consisting of cobalt, tantalum andtitanium and mixtures thereof, or even stainless steel, is rotated in amanner to provide rolling engagement with the foil and slidingengagement with the grooved conductor, with the speed of rotation beinggeared to the rate of forward motion desired for said line of contact.To effect the desired bonding between the platinum metal foil and thesubstrate it is necessary to momentarily generate along said line ofcontact a glowing temperature sufiicient to soften but not melt thesubstrate surface. The heat build-up is a function of the time ofcontact at a particular bonding site and if the forward feed of the lineof contact is permitted to stop while the high kva. current is beingapplied, the resulting local overheating can melt or break through thethin platinum foil. It should be noted in this connection that the hightemperature generated along said line of contact is rapidly dissipatedwith normal movement of said line of contact due to the conductivity andhigh heat capacity of the lower massive conductor.

The rotation of the cylindrical element is adjusted to advance the lineof contact which a speed, generally 6 to 36 inches per minute to provideeffective bonding without danger of burn-through. Optimum speed with anapparatus of particular electrical output will vary depending upon thelength of the line of contact between the cylindrical element and theassemblage being bonded. By way of illustration an apparatus with anelectrical capacity of 58 kva. can bond approximately 16 square inchesper minute. This would mean if there is a one inch line of contactbetween the cylindrical element and the assemblage being bonded thisline of contact should be advanced at the rate of about 16 inches perminute, whereas with a line of contact /2 inch in length the speed ofmovement should be about 32 inches per minute.

The operator is assisted in selecting the proper forward speed for theparticular heating potential being applied by the characteristic glowingor bright red color in the area of said line of contact. The optimumtemperature generated in the vicinity of the line of contact should bein the softening range for the substrate metal and suitably within about100 to 500 degrees C. below the melting point for the substrate metal.Under a given set of conditions, however, it is desirable that pressure,electrical potential, and rate of movement of the line of contact bemaintained substantially constant for each pass over the foil-substrateassemblage, and for the several passes which may be necessary to fullycover the area of said assemblage.

The resulting bonded assemblage appears to be fundamentally differentfrom similar type assemblages prepared by methods heretofore available.At most of the interface between the platinum metal foil and thesubstrate there is an alloy zone that forms a strong mechanical bondbetween the two. This, alloy zone, however, extends only part waythrough the thickness of the foil and does not modify the chemicalnature of the outer surface of the foil. On the other hand, the highintensity heat and pressure may anneal the outer surface of the foil andgive the bonded assemblage a uniquely activated and continuous platinummetal surface.

In order to better visualize the mechanics of carrying out the presentmethod, attention is directed to the accompanying drawing in which anumber of adaptations of the method have been schematically illustrated,with essential parts of the apparatus identified by suitable referencecharacters in each of the views, and in which:

FIG. 1 is a side view of one type of apparatus setup taken in adirection axially of the cylindrical element.

FIG. 2 is a view substantially on the line 22 of FIG, 1.

FIG. 3 is a fragmentary view similar to FIG. 2 showing a modification.

FIG. 4 is a side view of another type of apparatus setup taken axiallyof the cylindrical element.

FIG. 5 is a view taken in the direction of the arrows 55 as seen in FIG.4.

FIG. 6 is an enlarged fragmentary sectional view of an edge portion of aplatinum metal-substrate assemblage.

FIGS. 7 to 9 are views similar to FIG. 6 showing various ways ofcovering edge and reverse side surface of the substrate.

In FIGS. 1 to 3 of the drawing the apparatus schematically illustratedis adapted for either power driven or manual operation. A massiveelectric conductor is employed in the form of a heavy bed 10 of copperor suitably a somewhat harder copper alloy such as coppersilver orcopper-beryllium alloy. A 2% beryllium-copper alloy is especially hardand durable. Secured to the bed 10 is at least one and preferably aplurality of electrical leads 11 appropriate for applying the lowvoltage, high imperage current above mentioned to the bed 10.

A workpiece 12 in the form of a plate of tantalum,

titanium, niobium or an alloy thereof, is placed on the conductor bed 10and a coextensive or slightly larger sheet of platinum metal foil 13 islaid over the plate 12. The size and thickness of the plate 12 can bevaried within wide limits in preparing electrodes for different intendeduses. By way of illustration, electrodes for use in cells to chlorinateswimming pools, or sterilize domestic drinking water may use a plate 12measuring only about 2 inches by 6 inches and about thick, whereas forelectrodes intended to treat sewage or to be used industrially thesurface area may be several square feet with appropriately greaterthickness to provide the strength and stiffness desired.

At 14 is diagrammatically shown a movable, massive conductor suitablyfashioned from copper or copper alloy, as in the case of the bed 10,which is provided with an arcuate groove 15 to receive an elongated hardcylindrical conducting element 16 which is long enough to extend beyondthe edge of the bed 10, as seen in FIG. 2. The cylindrical element 16which, as previously mentioned, may be fashioned from various materials,such as tungsten, tungsten carbide or stainless steel is suitably of adiameter within the range of about inch to /4 inch, it being understoodin this connection that the smaller the diameter of the element 16 thenarrower will be the effective line or zone of contact as the element 16is pressed downwardly against the superimposed foil 13 and plate 12. Themovable massive conductor 14 is provided with at least one, andpreferably with a plurality of electrical leads 17. In fact, in order toaccommodate the required low voltage, high amperage current and stillprovide mobility in the conductor 14, it is preferable to employ aplurality of small flexible leads 17 since a single lead would generallybe so large as to interfere with movement of the conductor 14.

With a downward force W to compress the foil 13 and plate 12 between theelement 16 and bed 10, the element 16 is rotated in the direction of thearrow 18 at a speed to provide the desired advancing of the element 16in the direction of the arrow 19 so that under the influence of the lowvoltage, high amperage current applied to the leads 11, 17, the foil 13and plate 12 are bonded together beneath the advancing line of contactwith the element 16.

Factors to be considered in determining the proper downward force W,current applied to the leads 11, 17 and speed of movement in thedirection of the arrow 19 have been previously described and need not berepeated here. It is to be noted, however, that the application of theforce W in the control of movement in the conductor 14 and rotation ofthe element 16 can be effected either mechanically or manually dependingupon the size and number of plates 12 to be surfaced with platinum metalfoil 13. For purposes of illustration FIGS. 1 and 2 of the drawing maybe considered as representing a manually operated assemblage in which anoperator would hold the conductor 14 in one hand, applying the downwardforce W thereto, and with the other hand would rotate the element 16 bymeans of an offset crank 16(0) at one end thereof. When operated in thismanner the speed of movement in the direction of the arrow 19 iscontrolled by the rate of rotation of the element 16 by the hand crank16(a).

In FIG. 3 of the drawing there is shown a slight modification of thestructure of FIGS. 1 and 2 wherein the cylindrical element 16 has acentral portion of slightly enlarged diameter, as indicated at 16(b),which becomes the effective length of the element 16 for contacting thesuperimposed foil 13 and plate 12. With this adaptation the groove 15 inthe conductor 14 has an offset 15(a) to closely accommodate the largediameter portion 16(b) of the element 16, so that there is electricalcontact between the element 16 and the conductor 14 throughout theentire length of the groove 15, 15(a).

The modified construction of FIG. 3 can be advantageously used with bothmanually operated and power driven apparatus, and permits the apparatusto bond foil 13 to plates 1-2 of varying width by merely passing theassemblage through the apparatus a number of times to progressively bondthe foil 13 to the plate 12 along overlapping paths which aresubstantially the width of the axial length of the enlargement 1 6(b).By way of illustration, in a manually operated assemblage a rotatingelement 16 might be employed having an enlargement 16(1)) having anaxial length of one-half inch or slightly less, in which event four tofive passes over a plate 12 which is 2" wide, would permit bonding ofthe foil 13 across the entire width of the plate. In this instance afactor controlling the optimum axial length of the enlargement 16( b)could be the downward force W which could be effectively applied inmanual operation. On the other hand, with a mechanically drivenapparatus handling large electrodes for industrial purposes, where thewidth of the plate 12 might be one to two feet or more, a primary factorin determining optimum length of the enlargement 16(b) could be thepractical limitation on the supply of low voltage, high amperage currentto the leads 11, 17. In other words, it would be a matter of economicswhether the handling of wide plates 12 by several passes through theapparatus with a power source of moderate size might be more practicalthan a single pass operation which might require much largertransformers to provide adequate low voltage, high amperage current.

In FIGS. 4 and 5 there is diagrammatically shown a type of apparatuswhich is better suited to the quantity of mechanical bonding of foil 13to plates 12. In this type of apparatus the bed is replaced by a massiveconductor 20 in the form of a relatively large-diameter, rotatablecylinder fashioned from copper or copper alloy, as described inconnection with the bed 10*. In this type of apparatus the uppermlassive conductor 14 with the groove 15 to receive the rotatablecylindrical element 16 is supported in a manner to align the force W tothe axis of the element 16 and the axis of the cylindrical conductor 20in a common plane. The diameter of the cylindrical conductor 20 shouldbe ten to twenty times the diameter of the element 16 so that when aplate 12 and foil 13 are passed between the element 16 and cylindricalconductor 20 there is a substantially greater line or zone of contactwith the plates 12 than with the foil 13. Furthermore, the large mass ofthe cylindrical conductor 20 permits rapid flow of heat from the zone ofcontact with the plate 12.

The cylindrical conductor 20 and the upper massive conductor 14 areprovided with suitable leads 11, 17 respectively, for applying lowvoltage, high amperage current thereto, as above described, and there isdiagrammatically illustrated at 21 in FIG. 5 a drive and gear mechanismwhereby the cylindrical conductor 20 is rotated in the direction of thearrow 22, and the element 16 is rotated in the direction of the arrow 23at identical surface speeds while being electrically insulated one fromthe other. A support 24 is preferably employed to facilitate properaligning of the plate 12 and superimposed foil 13 as they are fedbetween the cylindrical conductor 20 and element 16, and a secondsupport 2-5 is also preferably employed to receive bonded articles asthey are delivered in the direction of the arrow 26.

The downward force W can be applied by any suitable mechanical linkage,hydraulic ram, or the like, appropriate for the size or width of plate12 to be handled. In this connection it will be noted that the width ofthe cylindrical conductor 20 and length of the element 16 can besubstantially varied depending upon the width of plates 12 to behandled. Furthermore, it is to be understood that the modification shownin FIG. 3 wherein the element 16 has a short axial portion of enlargeddiameter, which becomes the effective bonding portion thereof, can alsobe employed in the apparatus diagrammatically shown in FIGS. 4 and 5.

With the relatively smaller mass of the upper conductor 14 and theconcentration of heat in the vicinity of the cylindrical element 16, itis sometimes desirable to provide passages 30- in the conductor 14 forcirculation of a cooling fluid. Such means for cooling the conductor 14would be of special value in an apparatus set-up intended for extendedperiods of continuous operation.

The conductor 14 may also be subject to wear or scaling within thegroove 15, 15a, particularly when the conductor is made of copper. Thiscan be minimized by switching to the use of harder alloys of copper asabove mentioned, or by using other conductive materials such astantalum, rhodium, gold or their alloys in at least the portions forminginner surfaces of the groove 15, 15a.

The enlarged showing in FIG. 6 illustrates an edge portion of a plate 12bonded to foil 13' with the zone of weld or bond indicated at 27. Inmany instances 'where a platinum metal is bonded to a plate of titanium,niobium or tantalum, the edge 12(a) and reverse side 12(b) of the platemay simply be left uncoated, thereby providing in effect an electrodehaving one operating surface. Alternatively, the edge 12(0) and reverseside 12(b) can be coated with a protective film 28 of epoxy resin,glassy ceramic, or other non-metallic material. For other electrode usesit may be preferable to fold the foil '13 around the plate edge 12(a)and under the reverse side 12(1)), as seen at 13(a) in FIG. 8, in whichevent the portion 13(a) can be bonded to the reverse side 12(b) of theplate using apparatus of the type above described but with the portion13(a) engaged by the element 16 or enlargement 16(b) thereof. Here againa coating 28-(11) of epoxy resin, glassy ceramic or the like, can beapplied, if desired, to portions of the plates 12 which are not coatedwith platinum metal.

In some types of electrolytic processes it is desired that both surfacesof an electrode be active surfaces. In such event a second platinummetal foil 13' can be applied to the reverse side 12( b) of thepreviously bonded assemblage using the apparatus above described withthe foil 13' in contact with the element 16 or enlargement 16(b)thereof. It should be noted in this connection that in a second pass ofthe assemblage through the apparatus heat is conducted sufficientlyrapidly away from the bonding site by the bed 10 or cylindricalconductor 20 so that little or no change is effected in the previouslybonded platinum metal layer. In other words, the bonding heat iseffectively concentrated at a limited zone in which the element 16, orenlargement 16(b) thereof, is in engagement with superimposed foil andthe plate 12. A double face assemblage, such as shown in FIG. 9, canhave the edge portions sealed in various ways. Overlapping edges ofthefoils 13, 13' can be brought together and welded as seen at 29 oralternatively a film 28(1)) of epoxy resin, glassy ceramic, or otherprotective nonmetallic material can be applied.

While in the foregoing description reference has been made to thebonding of platinum metal to plates or substrates of tantalum, titanium,niobium and their alloys, (a typical alloy being -85% titanium and20-15% molybdenum), it should be noted that the method is also effectivein bonding platinum metals to other substrates including aluminum,nickel, and certain stainless steels. These other metals, which might beclassed as compatible metals, apparently enter into suflicient alloyformation 'with the platinum metal to securely bond the continuousplatinum metal foil to the substrate when assembled under the conditionswhich characterize the present invention. Thus, in its broad concept theinven tion is concerned with the bonding of platinum metal foil to anycompatible metal substrate. There is special advantage, however, whenproducting electrodes for use in electrolysis involving chlorineproduction or formation of hypochlorite or percompounds to employ assubstrate a metal such as tantalum, titanium, or niobium, or theiralloys, which are sufiiciently resistant to corrosive attack so thatlocal damage to a platinum metal coating will not lead to progressivedestruction of the electrode.

Laminated electrodes prepared in accordance with the present inventionhave been found superior to previously available electrodes in variouschlorinating and hypochlorinating treatments of water, including inparticular sterilization of drinking water, purification of swimmingpool water and treatment of sewage. Such electrodes are also superior inchlorite production, and in various fuel cells, electrodialyses, andelectro-organic reactions.

Various changes and modification in the method for preparing laminatedmetal articles and the laminated articles thus produced, as hereindisclosed, may occur to those skilled in the art, and to the extent thatsuch changes and modifications are embraced by the appended claims, itis to be understood that they constitute part of the present invention.

We claim:

1. The method of making electrodes that comprises bonding a platinummetal foil to a compatible metal substrate which is highly resistant toelectrolytic oxidation by applying along a line of contact between asmall diameter cylindrical member of hard conductive metal, rotatable ina massive electric conductor, in engagement with said foil, and a secondmassive electric conductor in engagement with said substrate, a pressureof about 10 to 300 pounds per linear inch, and an electric current below12 volts at an amperage to provide at least 3 kva. per linear inch ofsaid line of contact, while advancing said small diameter cylindricalmember in a direction perpendicular to said line of contact at a rate toprovide a bonding heat sufiicient to soften, without melting, thesubstrate surface.

2. The method as defined in claim 1, wherein the pressure applied iswithin the range of 50 to 150 lbs. per linear inch.

3. The method as defined in claim 1, wherein the voltage applied iswithin the range of 0.1 to 5 volts.

4. The method as defined in claim 1, wherein the applied electriccurrent provides 7 to 100 kva. per linear inch, and said line of contactis advanced at a rate to provide a temperature at the substrate surfacewhich is 100 to 500 C. below the melting point of the substrate.

-5. The method as defined in claim 1, wherein the pressure applied is 50to 150 lbs. per linear inch, the electric current is direct current of0. 1 to 5 volts and an amperage to provide 7 to 10 kva. per linearlinch.

6. The method as defined in claim 1, wherein the second massiveconductor is a fiat bed adapted to engage a large surface of the reverseside of said substrate.

'7. The method as defined in claim 1, wherein the second massiveconductor is a cylindrical rotatable body having its axis parallel tothe axis of said small diameter cylindrical member, and having adiameter 10 to 20 times the diameter of said cylindrical conductor.

8. The method as defined in claim 1, wherein said massive conductors areformed of a conductive metal selected from the group consisting ofcopper and highly conductive harder alloys of copper.

9. The method as defined in claim '1, wherein said small diametercylindrical member is formed of a hard conductive metal selected fromthe group consisting of tungsten, tungsten carbide, alloys of tungstencarbide, and stainless steel.

10. The method as defined in claim 1, wherein said small diametercylindrical member has a portion of slight- 1y enlarged diameter forengagement with said foil, the length of said large diameter portionbeing substantially less than the length thereof which is in rotatableengagement with the associated massive conductor.

11. The method as defined in claim 1, wherein the platinum metal in saidfoil is selected from the group consisting of platinum, rhodium,iridium, and ruthenium and alloys thereof.

12. The method as defined in claim 1, wherein the substrate metal highlyresistive to electrolytic oxidation is selected from the groupconsisting of tantalum, titanium, niobium and alloys thereof.

13. An electrode particularly adapted for anode use comprising alaminated body of a platinum metal foil bonded to a compatible metalsubstrate which is highly resistant to electrolytic oxidation preparedby the method defined in claim 1, the platinum metal of said foil beingselected from the group consisting of platinum, rhodium, iridium andruthenium and alloys thereof, the metal substrate being selected fromthe group consisting of tantalum, titanium, niobium and alloys thereof,and said laminated body being characterized by a bonding alloy zone atmost of the interface between said foil and substrate, and a smoothcontinuous outer surface on said foil which is unaltered by said alloyzone.

14. An electrode as defined in claim 20, wherein the substrate is a fiatplate with a platinum metal foil bonded to at least one fiat surfacethereof.

15. An electrode as defined in claim 20, wherein the substrate is a flatplate with a platinum metal foil bonded to at least one flat surfacethereof, and surfaces thereof not coated with foil are covered with anon-metallic protective film.

16. An electrode as defined in claim 15, wherein said non-metallicprotection film is an epoxy resin.

17. An electrode as defined in claim 15, wherein said non-metallicprotective film is a glassy ceramic.

18. An electrode as defined in claim 20, wherein the substrate is a fiatplate with a platinum metal foil bonded to opposed fiat surfacesthereof.

19. An electrode as defined in claim 20, wherein the substrate is a flatplate with a platinum metal foil bonded to opposed fiat surfacesthereof, and the edges are sealed with overlapping platinum metal foil.

20. An electrode comprising a laminated body of a platinum metal foilbonded to a compatible metal substrate which is highly resistant toelectrolytic oxidation prepared by the method defined in claim 1, saidlaminated body being characterized by a bonding alloy zone at most ofthe interface between said foil and substrate, and a smooth continuousouter surface on said foil which is unaltered by said alloy zone.

References Cited UNITED STATES PATENTS 5/1919 Palmer 219-82 Eldred29-l94 OTHER REFERENCES RICHARD M. WOOD, Primary Examiner.

B. A. STEIN, Assistant Examiner.

